My mother and her five brothers grew up in the tiny Boston suburb of Ashland, Massachusetts. Though Ashland is a mostly residential town, until 1978 it was home to Nyanza, one of the largest dye factories in the United States. A few years after Nyanza closed, it was discovered that the company had dumped more than 100 kinds of chemicals, including volatile organic compounds, mercury, and other products of dye manufacturing, into the surrounding ground and water. The Environmental Protection Agency designated the area as one of the 10 worst Superfund sites in the United States, and 20 years later nearby homes still have toxic vapors in their basements and the groundwater contains the carcinogen trichloroethene.

Last year a Massachusetts Department of Public Health study concluded there was a cancer cluster among Ashland kids who had grown up playing in the puddles around Nyanza and swimming or wading in the river at the spots where chemicals spewed from the plant. My uncle Chris used to play hockey on a Technicolor Nyanza pond, and my uncle Dennis ran through the stinking swamps during cross-country practice. Thankfully, neither of them remembers actually coming into contact with the water. We can't be sure about my uncle Brian's exposure to the water because we can't ask him. He died at age 42 of leukemia, an uncommon cancer for a young adult, several years before the study got under way.

Before he got cancer, Brian was a marathoner, a nonsmoker, bursting with health. When the study came out, some in my family were convinced that we had found the cause for his inexplicable illness, but others remained doubtful. I wasn't sure what to think. While I found the idea of resolution comforting—it would be nice to stop wondering "Why him?"—it was painful to imagine that something as innocent as playing in a river might have led to his death. The idea of Ashland's children being contaminated, unknowingly, irreversibly, when they were just starting out in life, broke my heart. So, uncharacteristically, I just stopped reading and thinking about it.

Then this past May the Silent Spring Institute came out with a report, sponsored by Susan G. Komen for the Cure, cata-loging what we know (and don't know) about environmental contaminants and breast cancer. Scientists calculated that, among the 216 possible mammary carcinogens identified by animal and human studies, 73 are in consumer products or food, 35 are in the air we breathe, and 29 are produced in this country in amounts exceeding one million pounds per year. That's just for breast cancer! Reading the list, I learned that this stuff is everywhere—in our furniture, homes, water, baby bottles, food, cleaning products, and air.

After a year of denial, suddenly I became obsessed. Many rates of both rare and common cancers, including breast cancer, have risen during the past quarter century. Some of the increase can be explained by better detection methods and the fact that we have a heavier, more sedentary population. However, some of it can't be explained, and scientists have started to look beyond environmental calamities like Nyanza to the inexorable buildup of chemicals in our bodies from everyday life.

Very little is known definitively about which chemicals are to blame. At the top of the suspect list are those capable of direct DNA damage and those called endocrine disruptors, which get into our bodies and may block our hormones or behave like their evil twins, encouraging cancer. Even when a carcinogen is identified, there are still questions to be answer-ed: Our genes likely play a role in how we metabolize certain substances, with some people succumbing to lower levels of contamination (in the Nyanza study, there was a two to three times greater than average risk of cancer for anyone who played in the water but a four times greater risk for those with a family history of cancer). There is a theory that chemicals may work synergistically, amplifying one another's negative effects, and evidence suggests that there may be a threshold at which chemicals accumulating in our bodies become deadly to us. Equally troubling, scientists say there may be critical periods when exposure is more dangerous, such as during puberty or pregnancy.

Breast cancer is one of the areas getting the most attention, especially given that the National Cancer Institute estimates that 90 percent of the roughly 200,000 annual breast cancer diagnoses are due to environmental and lifestyle factors (everything from what we breathe to where we work), not genes. It recently completed a major study on Long Island that concluded that PAHs, a by-product of fuel combustion in air pollution, produced a modest increase in breast cancer risk. (Note to self: Stop breathing.) The NCI is also sponsoring four Breast Cancer and the Environment Research Centers, which are investigating common chemicals that may lead to early menarche in girls—a risk factor for breast cancer.

When I spoke to Leslie Reinlib, director of the BCERC program, he told me reports from the puberty study ma y start trickling in this winter. "But I can't wait that long!" I almost screamed into the phone. After a week of late-night Internet research sessions, I was in a panic, afraid to wash my hair for fear my shampoo would cause breast tumors on contact. So I called Eric Winer, MD, director of the Breast Oncology Center at Boston's Dana-Farber Cancer Institute and chief scientific adviser to Komen. "These are all possible cancer-causing agents, but the operative word here is possible," he said. Instead of going nuts over factors that could potentially raise women's risk of breast cancer, he suggested I concentrate on what has been proven:

1. Don't get fat. In a Harvard study of 87,000 women last year, those who gained 55 pounds or more after age 18 had 1.45 times the risk of breast cancer after menopause as women who maintained a healthy weight.

5. Be a young mom. Having a child (or, better yet, a couple of kids) before age 30 reduces your risk.

This is all solid advice, but, to be honest, my first reaction to Winer's recommendations was disappointment. I already know I should be exercising and not getting bombed every night. What I need to know is whether I should burn down my house and live in an organically farmed grass hut. Then again, I'd been spending so much time researching carcinogens, I hadn't gone to the gym in a week.

So I went for a run...and then I called Jane Houlihan, PhD, vice president for research at the Environmental Working Group. EWG is a nonprofit that tracks what's in consumer goods and lobbies for tighter regulation. Houlihan couldn't say that my fears about chemicals were unwarranted, but she said, "We shouldn't feel guilty about the choices we make to live our lives. When you feel like it's overwhelming, just take a little piece. Do one thing at a time." Then she suggested three areas that account for most of our controllable exposures:

1. Drinking water. By-products of chlorination (to sanitize the water supply) may be implicated not only in breast cancer, but in bladder cancer, birth defects, and other illnesses. Plus, toxins from pesticides to industrial waste can end up in our drinking water. A carbon filter, either in a tabletop pitcher, attached to individual faucets, or on the main water line into the house will reduce your exposure.

2. Food. "The biggest concern is fatty meat and dairy products. So many chemicals we've produced historically, like DDT and PCBs, are really persistent in fatty foods," Houlihan says. She also suggests eating organically when possible. And, finally, be aware of what your food is packaged in. While plastics are indispensable, they can leach potential endocrine disrupters into food, such as phthalates and bisphenol-A. The most worrisome plastics are vinyl (sometimes indicated by a little recycling symbol with a "3" in it and found in many cling wraps), polystyrene and Styrofoam (indicated by a "6" and often found in clear takeout containers and foam meat trays), and polycarbonates (a "7" and found in some metal can linings and water cooler bottles). You can become too vigilant about this stuff. I told Houlihan that I was afraid to buy organic strawberries because they came in polystyrene; she told me to relax. "When it comes to getting your vitamins, organic berries are a good thing, even if they come in plastic."

3. Personal care products. While the FDA has declared low exposures to these ingredients safe, they are not subject to the same testing that drugs are, and scientists are still looking into their effects, especially on kids. Phthalates, which can be found in nail polishes, perfumes, and cleaning products (though they are rarely on ingredient lists), have been associated in some studies with abnormalities in infant boys' genitalia, damaged sperm, and early onset of adolescence in girls. Parabens are found in many lotions and shampoos as preservatives, and while their estrogenic effects are weak (10,000 to 100,000 times less than natural estrogen), their proliferation has raised concern. Houlihan also suggests avoiding triclosan, which is in many antibacterial soaps.

We may find after more research that these chemicals have little impact on our health. "We like to think they're harmless," Reinlib says. "And it's possible they are." So the final thing you can do to protect yourself and loved ones is to be aware of where your elected officials stand on the environment and medical research; know what's coming out of the smokestacks or being dumped behind local industries; and support cancer research. Because until we get more answers, we all just have to live with the not knowing.